We are studying regulation of the transcription and translation machinery in E coli. We are testing models of ribosomal RNA (rrn) operon regulation which include feedback inhibition of rrn transcription by free ribosomes and the presence of an antitermination system in rrn expression. We ask whether there are differences in expression between the seven rrn operons. We are also examining the possible role open reading frames (ORFs) adjacent to rrn operons play in rrn expression. In these studies we will use fusions, in which an rrn control region regulates the expression of gene(s) fused to it. These fusions provide a way of studying and manipulating an isolated control element so that a combination of physiological and genetic techniques can be applied to the control region of a single rrn operon. We have fused each of the seven rrn control regions to the gene for chloramphenicol acetyltransferase (CAT). The plasmids also contain the gene encoding Beta-lactamase and we use assays of Beta-lactamase as an internal control. These fusion plasmids will be used for in vitro mutagenesis and selection of rrn control mutants. Such mutant studies are important to delineate specific regulatory features. Our interest in control of the transcription machinery centers on the RNA polymerase subunits Beta and Beta'. These subunits are cotranscribed with several ribosomal protein genes. An attenuator between the rpl and rpo genes results in an BO percent drop in transcription of the rpo genes with respoect to the rpl genes. Under some conditions, this difference is eliminated. We would like to know whether this increased expression of the rpo genes is due to modulation of the attenuator or the activation of promoters. We also intend to make a transcription survey of the entire rplKAJL-rprBC transcription unit. S1 mapping and filter hybridization of labeled mRNA will be used to address these problems.